It completely depends on the quality of the materials used to make the sleeping bag or blanket. What you are looking for is to find a material that is a good insulator (poor conductor of heat). When you wrap it around your body, the own heat your body is producing is trapped for a period of time in the area between your body and the blanket and you feel warmer than you would without the blanket (where the heat from your body would rapidly escape out into the colder surroundings).

Using more blankets is like adding more insulation to your roof. Yeah, in principle this can make you "more warm" (the layer of thickness of the insulating material lowers the rate of heat loss to the surroundings even more up to a point), but there comes a point when the extra blankets are cumbersome. Rather than use more blankets, you could just make one blanket made out of a better (usually more expensive...) insulating material (like down feathers inside the blanket instead of cotton) and you could get the same benefit from one layer of a good blanket (or sleeping bag or whatever you choose to make out of it) as you could from several cheap ones stacked on top of each other (and in this sense you were correct). The rich people climbing everest have the money to take this approach, not to mention the benefit of carrying less weight with one sleeping bag vs. many blankets...

You can also tell her that you don't necessarily need blankets to improve your bodies resistance to heat loss, because it turns out that fat is an excellent insulator. Many animals such as polar bears for example have thick layers of fat to keep their insides from freezing over in the arctic. So all you have to do is to eat lots of food and become obese, and you can improve your resistance to heat loss before you even get to the question of using a sleeping bag or a blanket! Of course, you would have trouble climbing everest if you were obese...

I'd propose an analogy: What's heavier; an apple or a peach? It depends!

The best sleeping bags are better at keeping a mountaineer warm on Everest because that's what they've been designed for. A load of blankets would be just as good, but the mountaineer would have a really hard time carrying them up, and they'd probably get wet, and then they wouldn't work so well.

Maybe someone can help me settle an argument. Here's the converation:
Friend: If you're cold in bed, just put on more blankets. Adding more blankets will get you warmer.

Me: What about someone hiking Mt. Everest, who needs something that could handle -300 degrees. Should they just bring along a bunch of blankets?

Friend: Yeah, that would work. It just takes less space to bring sleeping bags, that's why they bring sleeping bags.

Me: I think the reason they bring sleeping bags is that they are more efficient than blankets.

So, are sleeping bags used only because they take up less space, or are they more efficient?

What do you mean by "more efficient"? The only definition of "more efficient" for blankets and sleeping bags is to give more warmth for the samw volume or weight- in other words, here, "more efficient" and "take up less space" mean exactly the same thing.

However, in reading some of the other posts, I'm wondering this. It's suggested that sleeping bags for Mt. Everest be rated at -300. Now, could you really pile on enough blankets to keep yourself warm at -300? Would it take so many blankets that you would be crushed first?

However, in reading some of the other posts, I'm wondering this. It's suggested that sleeping bags for Mt. Everest be rated at -300. Now, could you really pile on enough blankets to keep yourself warm at -300? Would it take so many blankets that you would be crushed first?

No prob This is my last day on here for awhile so I am glad that at least something I wrote is of use.

You certainly could pile on enough blankets to keep yourself warm at "-300" or whatever, but the point I was trying to make is you can instead use ONE blanket made out of better material to keep yourself just as warm at "-300." You can make this blanket out of the same material that you made any sleeping bag out of, couldn't you? In other words, the material that the sleeping bag or blanket is made out of determines how well it works, not the name "sleeping bag" or "blanket" itself (the only necessary distinction between these two is whether or not you sew a zipper on the side of your blanket and change the name to "sleeping bag" or if you do not).

The sad thing is you both tie when it comes to settling the argument because people that climb everest use sleeping bags over multiple blankets because there is a smaller size (so your friend is correct), AND they pay the big money so that their sleeping bag is way better at holding in heat than the average blanket you might buy at target (so they don't need "multiple sleeping bags" to achieve the same effect...so you are correct).